Untitled Quiz

Liver Functional Anatomy

• Located in the dome of the diaphragm within the abdominal cavity
• Has four main lobes (left, quadrate, right, and caudate)
• In some animal species, the left and right lobes have medial and lateral sections
• The caudate lobe has caudate and papillary processes
• The liver's position allows for movement due to diaphragm
• The gall bladder is present in some animals (carnivores, ruminants, pigs, mice) but not in others (horses, rats). Bile is still produced but not stored in these species.

Liver Histology

• A fibrous capsule surrounds the liver, extending into the liver tissue forming branched septa
• These septa demarcate functional units called hepatic lobules
• Hepatocytes are the primary functional liver cells; they absorb molecules from the space of Disse through the sinusoidal membrane.
• Bile canaliculi are the spaces between hepatocytes where bile is secreted, and are part of a network leading to larger bile ducts

Biliary System

• Bile travels from the liver to the duodenum
• Bile is secreted across hepatocyte membranes into canaliculi then small bile ducts
• These ducts anastomose into larger ducts that coalesce to form hepatic bile ducts
• The bile duct enters the duodenum via the sphincter of Oddi
• Bile moves between the gall bladder and bile duct via the cystic duct

Blood Supply of the Liver

• The hepatic portal vein supplies 75% of the liver's blood
• The hepatic artery supplies the remaining 25%
• Blood from both sources mixes in sinusoids (venous and arterial blood)
• Sinusoids empty into central veins
• Central veins combine to form hepatic veins, which drain into the caudal vena cava

Liver Functions Summary

• Detoxification of wastes, xenobiotics, and drugs
• Synthesis of cholesterol and bile acids
• Synthesis of plasma proteins
• Breakdown of red blood cells (erythrocytes)
• Carbohydrate, lipid, and amino acid metabolism
• Removal of bacteria (by Kupffer cells)
• Storage of glycogen, iron, copper, and vitamins

Liver Metabolism

• Carbohydrate metabolism (glycogenesis, glycogenolysis, gluconeogenesis)
• Lipid metabolism (fatty acid oxidation, ketone bodies, cholesterol, phospholipids, bile acid synthesis)
• Protein metabolism (deamination, transamination of amino acids, synthesis of non-essential amino acids)

Hepatic Lobule

• Shaped like hexagons
• Consists of hepatocytes radiating out from a central vein
• Portal triads (bile duct, hepatic artery, hepatic portal vein) are located between lobules

Hepatic Acinus

• A functional unit within the liver
• Divided into zones based on their distance from the arterial blood supply
• Zone 1 cells are closest to the artery and have the best oxygen supply.
• Zone 3 cells are furthest from the artery and have the poorest oxygen supply.

Liver Role in Detoxification and Clearance

• Purifies, transforms, and clears substances from the gastrointestinal tract (entering via hepatic portal vein)
• Converts harmful substances into less harmful ones
• Hepatocyte microsomes contain enzymes that oxidize substances (cytochrome P450) for further degradation or conjugation to make them water-soluble for excretion

Liver Role in Erythrocyte Breakdown and Bile Excretion

• Red blood cells (RBCs) are broken down by macrophages in the spleen and liver
• Hemoglobin is broken down to yield heme and globin
• Heme is converted to biliverdin, then to bilirubin
• Bilirubin is transported to the liver, conjugated, and excreted into bile
• Bilirubin in the gut is metabolised by bacteria to stercobilin which gives feces its colour.